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Acrophyseter
''Acrophyseter'' is a genus of stem-sperm whales that lived around 6 million years ago, found in the Pisco Formation in Peru.〔
==Description==
''Acrophyseter'' is derived from the Greek ''akros'', meaning ''acute'', which describes the short, pointed upturned snout, and ''Physeter'', the scientific name for sperm whales. But unlike today's sperm whales, ''A. deinodon'' was relatively small at around 4 m (13 ft) and had teeth on both the upper and lower jaws; 12 pairs in the upper jaw and 13 pairs in the lower. These teeth were large, sharp, and set firmly in deep sockets; the species epithet ''deinodon'' is from the Greek ''deinos'', meaning terrible, and ''odon'', tooth. The lower back teeth were close together suggesting they were used for shearing, unlike the suction feeding used by today's sperm whales, which don't even have teeth on their upper jaws. These differences imply that ''Acrophyseter'' fed on comparatively large prey, such as the smaller whales like ''Piscolithax'', pinnipeds like ''Acrophoca'', and penguins like ''Spheniscus urbinai'' that lived in the area at that time.
Various skull characteristics such as the size of the teeth and presence of tooth enamel which living sperm whales don't have indicate that ''Acrophyseter'' is probably a sister group to the ''Brygmophyseter'' and ''Zygophyseter'' group and to the group comprising ''Aulophyseter'' and living physeteroids, the kogiids and physeterids.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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